The references cited in this Background section and in the Description that follows are to provide a better understanding of the invention described herein after, as a resource for materials and methods that may further enable one to practice the methods and/or obtain the compositions later described herein, and as an abbreviation for such methods. Accordingly each reference cited herein is incorporated by reference to the extent the references provide a teaching that aids in the making and using of the invention later claimed. If there is any conflict in the disclosure provided herein and the cited references, the present disclosure controls over the teaching of the cited reference to the extent they conflict. The citation of a reference anywhere herein is not an admission that such a reference is pertinent to, or prior art to the invention claimed hereafter.
Hansenula polymorpha is a yeast species of both industrial and scientific importance. This non-conventional thermotolerant methylotrophic yeast is one of the best yeast systems for the production of heterologous proteins (Gellissen, 2000; Gellissen, (ed.), 2002; Suckow and Gellissen, 2002), it serves as a model to study peroxisome function (Van der Klei and Veenhuis, 2002), methanol metabolism, nitrate assimilation (Siverio, 2002) and stress responses (Ubiyvovk et al., 2006). H. polymorpha also has potential to be useful in biofuel production by fermentation of lignocellulosic carbon sources because it is able to ferment xylose (Ryabova et al., 2003), and is one of the most thermotolerant of yeast species (Guerra et al., 2005). However H. polymorpha's utility as an organism to produce ethanol by fermentation may be limited because its growth is rather sensitive to ethanol in comparison to other yeasts, such as S. cerevisiae. 